Titanium accelerated oxalate metal coating compositions and method of coating



United States Pate fQ TITANIUM ACCELERATED' OXA LATE COATING COMPOSITIONS AND ll/IETHOD OF COATING Edwin W. Goodspeed, Royal Oak, andRobert C. Gibson, Birmingham, Mich., assignors to Parker Rust Proof Company, Detroit, Mich, a corporation of Michigan No Drawing. Application December 31 1952*, Serial No. 329,110

Claims. (Cl- 148 -614) .The present invention relates to coatings for metallic surfaces which are primarily useful in protecting those surfaces during chemical Working operations, but which are also beneficial in increasing resistance to corrosion andas a base for paint. More particularly this invention concerns oxalate metal coatings and novel compositions'for forming the same.

It is now well-known thatferrous oxalate coatings are formed on mild steel surfaces by contacting those surfaces with heated aqueous oxalic acid solutions or with aqueous oxalic acid solutions which are maintained at temperatures as low as room temperature if the solution contains a suitable oxidizing agents or agents. Among the known agents which are suitable for thispurpose are hydrogen peroxide, manganese dioxide, sodium sulfite and ferric ion. Metals other than mild steel, and particularly those metals which resist corrosion, are not successfully coated with coatings of. commerciaI quality by such solutions. U. S. Patent 2,577 ,887 discloses that the presence of an anion selected from the group consisting of chloride, bromide, thiocyanate and ferricyanide, suihciently activates an aqueous oxalic acid solution containing the ferric ion so that high quality coatings are obtained on stainless steels.

The present invention is concerned with anew composition of the general type which is disclosed in U. S. Patent 2,577,887. The composition of this invention is useful in producing adherent commercial quality oxalate coatings on said steel, stainless steel, and a wide variety of additional substrate metals as discussed more fully hereinbelow. This invention is based on the discovery that titanium is useful as an accelerator in an aqueous oxalic acid solution.- Titanium serves to increase the attack of thesurface by the oxalic acid so that oxalate coatings are formed on surfaces which are easily coated as well as those which are normally resistant to attack by an aqueous oxalic acid solution. Titanium has been, found to be unexpectedly effective in increasing the rate of attack of oxalic acid on normally resistant metals and is; useful in amounts as low as- .025 of the amount of ferric ion which is set forth as useful in U. S. Patent 2,577,887.

Broadly, the compositions of the present invention comprise as the essential coating-producing ingredients, an aqueous solution of oxalic acid and titanium. More specifically, the compositions of this invention comprise. as the essential coating-producing ingredients, an aqueous solution of oxalic acid, titanium, an oxidizing agent and an activating anion, the oxidizing agent being present in an amount equivalent to about 0.08% to .5% chlorate, and the activating anion being present inan amountsequivalent to at least about 2.2% chloride. I

The compositions of this invention have been found to produce useful adherent oxalate coatings on the surfaces of mild steel, stainless steel, iron, copper, aluminum, nickel and chromium and the'alloys of iron, copper, aluminurn, nickel and chromium. The term-stainless steel is used herein in its generally accepted meaning. A .dBe

2,785,097 Patented Mar. 12,

tailed list of: steels which come under the term stainless steel can be found on pages 554'- and 55-5 of: the 1948 edition of the Metals Handbook, published by' the American Society for Metals.

For coating mild steel and other metals which are readily attacked by heated oxalic acid, an aqueous acidic solution containing at least 2% oxalic acid up to saturation, and at least .0001% titanium up to saturation, is satisfactory. Such a solution may be operated at'any desired temperature between room temperature and the boiling point of the solution, but the presence of titanium renders unnecessary raising the temperature of theso'lution above about 120" F. thereby reducing. the problems and difiiculties which are inherent in the operation ofan elevated temperature solution. 1

Titanium may be introduced-into the aqueous oxalic acid solution in the form of any soluble salt, the anion portion of which is not incompatible-with the solution or which forms an undesirable component of the coating itself; Suitable: titanium solts which have been found to be sufficiently soluble to introduce the requisite quantityof titanium into the solution, include TiF4, TiCl4,

Potassium titanium oxalate being a source for both the oxalafe. ion and titanium and due to its availability and solubility, is the preferred source of titanium.

For coating metals more resistant to attack by oxalic acid, the above solution is preferably modified to contain a conventional oxidizing agent such, as chlorate, nitrate, nitrite, hydrogen peroxide, sodium meta nitro benzene sulfonate or picric acid, and an auxiliary activator such as fluoride, chloride, bromide or thiocyanate. Suitable ranges of proportions of the ingredients of the modified composition are given in Formula I. The compositions of Formula I will be understood to be suitable for use in producing oxalate coatings on any of the hereinabove enumerated substrate metals. Proportions of ingredients as set forth in Formula I refer hereinafter in this specification and in the appended claims, to percentage by Weight per volume unless otherwise specified.

FORMULA I Concentra- Concentration Useful tion Pre Ingredient Range t'erred- Range, percent Oxalie aci 1 .27 to saturation 2-16 Titanium nu .000l% to saturation" (ll-1.5 Chloride anion" 2.2% to saturation" 4-8 Chlorate aniom- 08% to .5% 3-. 6

In a composition containingthe proportions of oxalic acid and titanium as set forth in Formula I, the chlorate anion can be replaced by other oxidizing agents and in the ranges of proportions as set forth in Table I; It will be understood that the oxidizing agents set forth in T ablel have an effect on the coating characteristics of the solution which is comparable or equivalent to the effect caused by the chlorate anion in the range of proportions set forth considered conventional oxidizing agents in both zinc phosphate and alkali metal phosphate solutions are suitable for' use in the compositions of this invention. For example, potassium d-ichromate, sodium nitrite, potassium bromate and sodium chlorite have been found to be of little usefulness. Ceric sulfate is unsuitable because it forms an insoluble precipitate. Sugar, iodine and formaldehyde are likewise unsuitable for use.

The chloride anion as set forth in Formula I may also be replaced by other anions and in'the proportions set forth in Table II in a manner comparable to that explained above in relation to the chlorate anion. The anions set forth in Table II may be used as a substitute for the chloride anion and have a comparable or equivalent effect on the coating characteristics of the solution to that which iscaused by the presence of the chloride in the amounts set forth.

- Table 1] Concentration Useable Range Material The-ferricyanide ion when used alone was found to be ineffective in activating the compositions. The iodide ion is usable but is only slightly eifective and requires the presence of relatively large quantities on the order of about 70% and above.

Compositions containing proportions of titanium, chloride and chlorate within the preferred ranges set forth in Formula I, will form coatings on the more resistant metals at concentrations of oxalic acid as low as about .2%. However, for somewhat better commercial operation, it is preferable to maintain the concentration of the oxalic acid above about 2%. When the concentration of oxalic acid is between 2% and 16% and the chloride and chlorate concentrations lie within the preferred range of Formula I, the proportion of titanium which is required to produce a coating on difiicultly coated metals such as the stainless steels, is greatly reduced and a proportion as low as .0001% titanium is satisfactory. The coatings which are formed on the surface of stainless steels, for example, at concentrations of titanium of about .0001% are comprised of a dust layer and an adherent layer, the adherent layer being relatively light in weight and extremely suitable for use as a base for paint. As the concentration of titanium increases from about .002% up to about 1.5%, the weight of the adherent portion of the coating increases while the dust portion of the coating decreases. These heavier coatings provide increased resistance to corrosion and serve as an excellent surface protector during extreme deformation of the substrate metal. 7

The formation of an oxalate coating with the compositions of this invention on any of the metal surfaces hereinabove enumerated, is accomplished by contacting the metal surface with the aqueous composition at a temperature between room temperature and the boiling point of the composition for a short period of time on the order of 1 to 5 minutes. In the presence of the preferred quantity of titanium as set forth in Formula I, it is unnecessary to increase the temperature above about 120 to 125 F. in order to obtain a coating, but in order to further reduce the time required to form a coating and to maintain high quality in large scale production, it is' somewhat better to operate the solutions between about 125 F. and 170 F. A

A number of alternative composition formulas are given below by way'of illustration to exemplify a few of the many variations which the improved compositions of the invention may take within their operating range and to illustrate in greater detail the method of the invention.-

EXAMPLE I A 1 liter solution was made up containing .1% titanium as titanium oxalate, 5.0% chloride, .5 sodium chlorate and .2% oxalic acid. Test panels of AISI type 302 and 304 stainless steel were immersed in the solution for 5 minutes at 170 F. Typical dark green adherent oxalate coatings were formed on the surface. No'coating was formed on additional panels in other solutions identical to the above except that the concentration of oxalic acid was decreased below .2%.

EXAMPLE II grams sodium chloride, 1 gram sodium chlorate, and 1.5 grams potassium titanium oxalate were admixed with sufiicient water to make up to 200 ml. Oxalic acid was added to various portions of this solution to produce concentrations of oxalic acid of 2%, 4%, 6%, 8%, 10%, 12%, 14% and 16%. Type 302' stainless steel panels were immersed in each of these solutions for three minutes at 150 F. The coatings produced were dark green, adherent coatings comprising a dust portion and an adherent portion, the adherent portion of which increased in weight as the concentration of oxalic acid increased. The dust portion of the coating continually decreased as the oxalic water to make one liter. To various portions of this solution, quantities of potassium titanium oxalate were added to produce varying concentrations of titanium between .0001% and 2.5%. Type 302 stainless steel panels were immersed in the various solutions at .F. for three minutes and withdrawn. The coatings produced were relatively light in weight until the concentration of titanium reached about .002% at which concentration the adherent portion of the coating Weighed 75 mg. per square foot. As the concentration of titanium increased up to 1.5%, in graduated steps, the weight of the adherent portion of the coating increased to 595 mg. per square foot at 1.5% titanium. Representative titanium concentrations of this series and the resultant weight of coating obtained, are set forth in Table III.

Table III Dust Adherent Total Coat Coat Coating Percent Ti Mg] Mg] Wt., sq.ft. sq.ft. MgJ sq. ft.

Test panels of iron, copper, chromium, nickel Monel,

tions produces similar coatings.

What is claimed is:'

1. A composition of matter for producing an oxalate coating on a metallic surface which consists essentially of an aqueous solution containing'at least 0.2% of oxalic acid and titanium in an amount greater than .01%.

2. A composition of matter for producing an oxalate coacting on a metallic surface which consists essentially of an aqueous acidic solution of 2% to 16% oxalic acid and .01% to 1.5% titanium. a a

3, A composition of matter for producing an oxalate coating on a metallic surface which consists essentially of an aqueous solution of oxalic acid, titanium, an oxidizing agent and an activating anion, said oxalic acid being present in an amount from 2 to 16%, said oxidizing agent being present in an amount equivalent in its cfiect on the coating action of the solution to about 0.08% and 0.5% chlorate, said activating anion being present in an amount equivalent in its effect on the coating action of the solution to at least 2.2% chloride and said titanium being present in an amount greater than .01%.

4. A composition of matter for producing an oxalate coating on a metallic surface which consists essentially of an aqueous solution containing 2 to 16% of oxalic acid, titanium in a concentration between .01% up to saturation, the chlorate anion in a concentration between about .08% and 0.5% and the chloride anion in a concentration between 2.2% and saturation.

5. A composition of matter for producing an oxalate coating on a metallic surface which consists essentially of an aqueous solution of 2% to 16% oxalic acid, .01% to 1.5% titanium, 4% to 8% chloride anion and 3% to .5% chlorate anion.

6. A method for forming an oxalate coating on a metallic surface which comprise the steps of contacting the said metallic surface with an aqueous acidic solution containing at least 0.2% of oxalic acid and titanium in an amount greater than .01%, and maintaining the said solution in contact with said surface at a temperature between room temperature and boiling and until an adherent coating is formed.

7. A method for forming an oxalate coating on a metallic surface which comprises the steps of contacting the said metallic surface with an aqueous acidic solution of 2% to 16% oxalic acid and .01% to 1.5% titanium, and maintaining the said solution in contact with said surface at a temperature between room temperature and 170 F. and until an adherent coating is formed.

8. A method for forming an oxalate coating on a metallic surface which comprises the step of contacting said surface with an aqueous acidic solution maintained at a temperature between room temperature and 170 F. and containing as the essential coating-producing ingredients, oxalic acid, titanium, an oxidizing agent and an activating anion, said oxalic acid being present in an amount from 2 to 16%, said oxidizing agent being present in an amount equivalent in its effect on the coating action of the solution to about .08% to 0.5 chlorate ion, said activating anion being present in an amount equivalent in its eifect on the coating action of the solution to at least 2.2% chloride ion and saidtitanium being present in an amount greater than .0l%, until an adherent protective coating is formed thereon.

9. A method for forming an oxalate coating on a metallic surface which comprises the step of contacting said surface with an aqueous acidic solution maintained at a temperature between about and F. and containing as the essential coating-producing ingredients, oxalic acid in a concentration of from 2 to 16%, titanium in a concentration of 0.01% to 1.5 the chlorate anion in a concentration between about .08% and 0.5 and the chloride anion in a concentration between 2.2% and saturtion until an adherent protective coating is formed thereon.

10. A method for forming an oxalate coating on a metallic surface which comprises the step of contacting said surface with a composition at a temperature between about 125 and 170 F. and which consists essentially of an aqueous solution of 2% to 16% oxalic acid, .01% to 1.5% titanium, 4% to 8% chloride anion and 3% to .5 chlorate anion until an adherent protective coating is formed thereon.

References Cited in the file of this patent UNITED STATES PATENTS 1,723,067 Pacz Aug. 6, 1929 2,516,008 Lum July 18, 1950 2,577,887 Gibson Dec. 11, 1951 

1. A COMPOSITION OF MATTER FOR PRODUCING AN OXALATE COATING ON A METALLIC SURFACE WHICH CONSISTS ESSENTIALLY OF AN AQUEOUS SOLUTION CONTAINING AT LEAST 0.2% OF OXALIC ACID AND TITANIUM IN AN AMOUNT GREATER THAN .01%. 